A sliding nozzle apparatus is configured such that one of two or three refractory plates having a nozzle hole is slidingly moved while they are clamped at a high pressure (while they are applied with a surface pressure therebetween), to thereby change a degree of opening of the nozzle hole to control a flow rate of molten metal. This slidingly-movable plate (i.e., sliding plate) is held by a slide metal frame, which is provided in an openable and closable manner so as to enable the sliding plate to be replaced with a new one.
The sliding plate reaches its usable life after it is used only several times. Thus, there is a need to replace the sliding plate with a new one or check a damage state of the sliding plate, by opening the slide metal frame. In this case, it is necessary to release the surface pressure before opening the slide metal frame, and then apply the surface pressure again after closing the slide metal frame.
As a way to apply and release the surface pressure in the sliding nozzle apparatus, there has been known a technique of applying and releasing the surface pressure by means of sliding movement (sliding displacement) of the slide metal frame. That is, this technique is configured to cause a spring to be deformed by using a driving force during sliding movement of the slide metal frame. In this technique, a slide range (movable range) of the slide metal frame during an operation of applying or releasing the surface pressure is set to go beyond a slide range during a casting operation. For this reason, in case of using two types of drive units having different strokes between during the casting operation and during the surface pressure applying/releasing operation, there is a problem of increased cost due to requiring two drive units.
On the other hand, there has also been proposed another technique of switchably changing the coupling position between the drive unit and the slide metal frame, by using one drive unit.
For example, the following Patent Document 1 discloses a coupling position switching technique configured to couple a drive unit and a slide casing (slide metal frame) through a guide piece, and switchably change a coupling position between the drive unit and the guide piece within an opening defined in the guide piece, by using a coupling position switching means. This guide piece is configured to be moved linearly based on a guide rail provided on a base frame, and an extension guide disposed to be slidingly moved along the guide rail in an extendable manner.
More specifically, in the second embodiment of Patent Document 1, as depicted in FIG. 16, the coupling position switching means 20 is a rectangular shaped bar as whole as viewed in a plane, and is provided with a semi-cylindrical recess 20a and a handle 20b. At both ends of the recess 20a, a first and second counterbore portions 20aA, 20aB are formed, which have diameters greater than that of recess 20a. The counterbore portions 20aA, 20aB are configured such that the protruding portion 7e located at the distal end of the rod 7A as described herein below is engaged inside the counterbore portions.
In first coupling position as depicted in FIG. 17, this coupling position switching means 20 is arranged between the coupling member 7a of the drive unit 7 and a first positioning surface a of the opening 25, in the second coupling position (not depicted), the coupling switching means 20 is arranged between the protruding portion 7e of the coupling member 7a and a second positioning surface b. In addition, as depicted in FIG. 18, it is described that the connecting switching means 20 is moved up and down in the direction of arrows A and D and the rod 7A is moved in the direction of arrow B or E so that the position of such coupling position switching means 20 is changed.
However, according to the technique disclosed in Patent Document 1, the driving force caused by forward and backward movements of the rod 7A is adapted to be transmitted to the slide casing 4 via the coupling position switching means 20 and the guide piece 24, in this case, the coupling position switching means 20 is merely brought into contact with the guide piece 24. As such, there is a problem in the reliability and smoothness of transmission of the driving force to the slide casing 4 according to the forward and backward movement of the rod 7A.
Furthermore, the coupling position switching means 20 is a spacer as an extension means of the rod 7A which is inserted between the front face of the head of the rod 7A and the inner wall face of the space or between the rear face of the head of the rod 7A and the space. As such, this coupling position switching means 20 requires to put it in two positions (a first coupling position and a second coupling position) during the surface pressure applying/releasing operation and during the casting operation (during use), so the operation becomes complicated, and the coupling position switching means is likely to be inserted in the wrong position. Moreover, due to a different arrangement position of the coupling position switching means 20 between the first coupling position and the second coupling position, it is not possible to hold the coupling position switching means 20 to the guide piece, and it is necessary to remove the coupling position switching means 20. As a result, the operation becomes complicated, and there is also a problem that the coupling position switching means 20 is easy to be lost.
Further, in Patent Document 1, the rod 7A and the slide casing 4 are connected via the guide piece 24. The guide piece 24 is configured to be moved linearly based on a guide rail provided on a base frame, and an extension guide disposed to be slidingly moved along the guide rail in an extendable manner. Therefore, the connecting structure via the guide piece 24 becomes complicated and increases in size. In addition, the guide piece 24 increases in size due to having a detachable portion with respect to the slide casing 4.